It is necessary to perform heat treatment at about 1600° C. in order to activate (diffuse or recrystallize) impurity ions implanted in SiC. However, there is a problem that an SiC surface remarkably becomes rough because sublimation of atoms or migration of surface atoms occurs in the SiC surface during the heat treatment.
Such surface roughness lowers the channel mobility of MOSFETs formed on the SiC surface, and deteriorates a gate oxide film. Additionally, in a Schottky barrier diode, such surface roughness may cause an increase in reverse leakage current or may cause variations in forward characteristics.
A method for forming a carbon film on an SiC surface prior to an impurity ions activation has been proposed as one method for solving this problem.
Patent Literature 1 (Japanese Patent Application Publication No. 2005-353771) discloses a method for manufacturing an SiC semiconductor device that includes a step of implanting impurity ions partly into an n-type drift layer to form an ion-implanted layer, a step of forming a carbon film on the n-type drift layer and on the ion-implanted layer according to a sputtering method, and a step of annealing the n-type drift layer at a temperature of 1600° C. or more when the n-type drift layer and the ion-implanted layer are covered with the carbon film.